This invention relates to photographic products and processes adapted to the provision of photographic images by diffusion transfer processing. More particularly, it relates to photographic processing compositions, film units and processes adapted to the provision of a diffusion transfer image retained within a permanent laminate and viewable through a transparent support against a reflecting background.
Diffusion transfer photographic products and processes have been described in the art and details relating to such products and processes can be found in numerous patents including, for example, in U.S. Pat. Nos. 2,983,606; 3,415,644; 3,594,165; and 3,647,437; and in Great Britain Pat. No. 1,220,524. In general, diffusion transfer photographic products and processes involve film units having a photosensitive system including at least one silver halide emulsion layer usually integrated with an image-providing material. After photoexposure, the photosensitive system is developed to establish an imagewise distribution of a diffusible image-providing material, at least a portion of which is transferred by diffusion to an image-receiving layer capable of mordanting or otherwise fixing the transferred image-providing material. In some diffusion transfer products, the transfer image is viewed by reflection after separation of an image-receiving element from the photosensitive system. In other products, such separation is not required and the transfer image is viewed against a reflecting background, usually provided by a dispersion of a white, light-reflecting pigment such as titanium dioxide.
A number of photographic products and processes have been proposed for providing diffusion transfer photographic images retained as part of a permanent laminate. Typically, a photographic laminate will comprise a pair of outer polymeric layers, e.g., polyester, having therebetween a developed photosensitive system and a suitable image-carrying layer. In such photographs, the image-carrying layer is separated from the developed silver halide photosensitive system by a light-reflecting layer (e.g., a layer containing titanium dioxide positioned between the developed silver halide emulsion system and the image-carrying layer) and at least one of the outer polymeric layers is transparent to permit viewing of the photographic image against the light-reflecting layer. Diffusion transfer photographic products which provide a permanent photographic laminate as described are known in the art as "integral negative-positive film units" and illustrations thereof can be found, for example, in the above-noted U.S. Pat. Nos. 3,415,644; 3,594,165; and 3,647,437.
In the processing of certain preferred diffusion transfer film units adapted to the provision of a permanent photographic laminate, it has been customary to effect photographic development with the aid of an aqueous alkaline processing composition including a light-reflecting agent, e.g., titanium dioxide. Such a processing composition is typically spread from a rupturable container by passage of the film unit between a pair of rollers so as to distribute a layer of processing composition between the sheet elements of the film unit. The distributed layer of processing composition upon drying forms a light-reflecting layer which provides a background for viewing of the photographic image and serves to bond the layers of the film unit together to form the desired permanent laminate. Photographic processing compositions suited to such purposes are described, for example, in the aforesaid U.S. Pat. Nos. 3,415,644; and 3,647,437. As is pointed out in these patents, a viscosity-increasing agent is usually included in such processing compositions to facilitate uniform spreading of the composition, e.g., a polymeric film-forming material such as hydroxyethyl cellulose or carboxymethyl cellulose.
Photographic processing compositions including a polymeric oxime viscosity-increasing agent are described in U.S. Pat. No. 4,202,694 (issued May 13, 1980 to L. D. Taylor). While the polymeric oxime viscosity-increasing agents of the patent afford certain advantages as described therein, and notably from the standpoint of permitting favorable dye transfer rates in diffusion transfer processing, adhesion or cohesion failures in the dried light-reflecting layer formed from the distributed processing composition may be observed. Typically, the adhesion or cohesion failure will result from physical abuse of the photographic laminate, such as may be induced by bending, folding or curling the photograph.
Generally, the photographic laminate will be provided with a suitable frame or border which, for example, may be comprised of fold-around tape fastened about the perimeter of the photographic laminate to the top and bottom laminar elements, or which may comprise rail elements adhered between the laminar elements about the perimeter of the photograph.
The frame has an aesthetic purpose, provides a measure of rigidity or reinforcement to the photographic laminate and serves to confine the laminar elements of the photograph within a border which prevents easy separation of the laminated elements. Physical abuse of the photograph may nonetheless cause a separation or delamination of the image-receiving element from the deposited and dried light-reflecting layer. Adhesion failure may be manifested in the photographic laminate by an apparent pillowing effect. Moreover, discontinuities, resulting from a cohesion failure in the light-reflecting layer (manifested by localized and preferential adhesion of light-reflecting material to the separated image-receiving element), may also be observed.
Attempts to alleviate the problems associated with adhesion or cohesion failure may in turn result in loss of certain advantages, e.g., favorable dye transfer. It will be appreciated that the reduction of such separation or delamination occurrences without adverse influence on favorable dye diffusion transfer is to be desired.